When connecting to a dashboard for the first time, Tableau normally will be querying the actual data source to render the view.. After that, requests will use cached results, which will generally be quicker.

The cache with then expire after a period of time (depending on what has been configured on the server), which is why the next day the first request again takes longer to run than subsequent ones.

From the link you sent, Russell was saying that "Refresh less often" option will cache data up to 12 hours. However from onlinehelp, Configure Data Connections , it will last as long as nothing changes or i misunderstood the statement?

Refresh Less Often—Data is cached and reused whenever it is available regardless of when it was added to the cache. This option minimizes the number of queries sent to the database. Select this option when data is not changing frequently. Refreshing less often may improve performance.